/**
*      author: Y_Yao
*      created: 2025-03-22 20:07:15
**/

#include<bits/stdc++.h>

#define int LL
using namespace std;
using LL = long long;
const LL LLINF = 9e18;
const int INF = 0x3f3f3f3f;
const int N = 3e5 + 7;
int a[N];
int n;

map<int,int,greater<int>> mp;
unordered_map<int,int> mp2;

void solve()
{
    cin >> n;
    for(int i = 1;i <= n;i++)
    {
        cin >> a[i];
        mp[a[i]]++;
        mp2[a[i]] = i;
    }
    int ans = 0;
    for(auto& e : mp)
    {
        if(e.second == 1)
        {
            ans = mp2[e.first];
            cout << ans << endl;
            return;
        }
    }
    cout << -1 << endl;
}

signed main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);

    int t = 1;
    //cin >> t;
    while(t--)
    {
        solve();
    }
    return 0;
}